A. Human Immune Interferon
Human interferons can be classified in three groups on the basis of different antigenicity and biological and biochemical properties.
The first group comprises a family of leukocyte interferons (.alpha.-interferon, LeIF or IFN-.alpha.), which are normally produced mainly by constituent cells of human blood upon viral induction. These have been microbially produced and found to be biologically active (1, 2, 3). Their biological properties have prompted their use in the clinic as therapeutic agents for the treatment of viral infections and malignant conditions (4).
In the second group is human fibroblast interferon (.beta.-interferon, FIF or IFN-.beta.), normally produced by fibroblasts upon viral induction, which has likewise been microbially produced and found to exhibit a wide range of biological activities (5). Clinical trials also indicate its potential therapeutic value. The leukocyte and fibroblast interferons exhibit very clear similarities in their biological properties despite the fact that the degree of homology at the amino acid level is relatively low. In addition, both groups of interferons contain from 165 to 166 amino acids and are acid stable proteins.
The human immune interferon (.gamma.-interferon, IIF or IFN-.gamma.), to which this invention is directed, is, in contrast to the .alpha.- and .beta.-interferons, pH 2 labile, is produced mainly upon mitogenic induction of lymphocytes and is also clearly antigenically distinct. Until recently human immune interferon could only be detected in very minor levels, which evidently hampered its characterization. Recently, a rather extensive but still partial purification of human immune interferon has been reported (6). The compound was said to be produced from lymphocyte cultures stimulated with a combination of phytohaemagglutin and a phorbol ester and purified by sequential chromatographic separations. This procedure resulted in a product having a molecular weight of 58,000.
Human immune interferon has been produced in very low amounts by translating mRNA in oocytes, showing interferon activity characteristic of human immune interferon and expressing the hope that immune interferon cDNA could be synthesized and cloned (7).
The amount of immune interferon obtained until now is certainly insufficient to carry out unambiguous experiments on the characterization and biological properties of the purified component. However, in vitro studies performed with crude preparations, as well as in vivo experiments with murine .gamma.-interferon preparations, suggest that the primary function of immune interferon may be as an immunoregulatory agent (8, 9). Immune interferon has not only an antiviral and anticellular activity in common to all human interferons, but shows a potentiating effect on these activities with .alpha.- and .beta.-interferon (10). Also, the in vitro antiproliferative effect of .gamma.-interferon on tumor cells is reported to be approximately 10- to 100-fold that of the other interferon classes (8, 11, 12). This result, together with its pronounced immunoregulatory role (8, 9), suggests a much more pronounced antitumoral potency for IFN-.gamma. than for IFN-.alpha. and IFN-.beta.. Indeed, in vivo experiments with mice and murine IFN-.gamma. preparations show a clear superiority over antivirally induced interferons in its antitumoral effect against osteogenic sarcoma (13).
All of these studies, until the present invention, had to be performed with rather crude preparations, due to the very low availability. However, they certainly suggest very important biological functions for immune interferon. Not only has immune interferon a potent associated antiviral activity, but probably also a strong immunoregulatory and antitumoral activity, clearly pointing to a potentially very promising clinical candidate.
It was perceived that the application of recombinant DNA technology would be a most effective way of providing the requisite larger quantities of human immune interferon. Whether or not the materials so produced would include glycosylation which is considered characteristic of native, human derived material, they would probably exhibit bioactivity admitting of their use clinically in the treatment of a wide range of viral, neoplastic, and immunosuppressed conditions or diseases.